1. Field of the Inventive Concept
The present invention relates to a non-volatile memory device, and more particularly, to a non-volatile memory device capable of being erased and programmed electrically.
2. Description of the Related Art
Semiconductor memories are a vital microelectronic component of digital logic systems, such as computers and microprocessor-based products ranging from satellites to consumer electronics. Therefore, advances in the design of semiconductor memories including fabrication process enhancements and technology developments providing higher densities and faster speeds help establish performance expectations for other digital components.
Semiconductor memory devices are classified as volatile random access memories (RAMs), or non-volatile memory (NVM) devices. In RAMs, the information (data) is stored either by setting up the logic state of a bistable flip-flop such as in a static random access memory (SRAM), or by the periodic refresh re-charging of a capacitor as in a dynamic random access memory (DRAM). In either case, the data are stored and can be read out only as long as the power is applied, and data are lost when the power is turned off; hence, they are called volatile memories.
Non-volatile memories, such as Mask Read-Only Memory (MROM), Programmable Read-Only Memory (PROM), Erasable Programmable Read-Only Memory (EPROM), and Electrically Erasable Programmable Read-Only Memory (EEPROM), are capable of storing data, even with the power turned off. The non-volatile memory data storage mode may be permanent or reprogrammable, depending upon the technology used. Non-volatile memories are used for program and microcode storage in a wide variety of applications in the computer, avionics, telecommunications, and consumer electronics industries. A combination of single-chip volatile and non-volatile memory storage modes is also available in devices such as non-volatile SRAM (nvSRAM) for use in systems that require fast, programmable non-volatile memory. In addition, dozens of special memory architectures have evolved which contain some additional logic circuitry to optimize their performance for application-specific tasks.
In non-volatile memories, however, MROM, PROM, and EPROM are not designed to be erased and written to by the system itself, so that it is not easy for users to update stored contents. On the other hand, EEPROM is capable of being electrically erased and electrically written. The EEPROM is typically applied as an auxiliary memory or in system programming where updates are needed (e.g., flash EEPROM).